Corning Incorporated, Corning, N.Y., has marketed photochromic glass lenses for at least 10 years which behave as filter glasses in exhibiting cut-offs of electromagnetic radiation at various specific wavelengths. Such lenses have been worn principally by persons requiring protection from ultraviolet radiation and have been marketed under such trademarks as CPF450 and CPF550, the number signifying a cutoff of radiation below 450 nm and 550 nm, respectively.
Those glasses had their genesis in U.S. Pat. No. 4,240,836 (Borrelli et al.) which describes a method for producing surface colored photochromic glasses which, in the undarkened state, exhibit red and purple colorations or mixtures of orange, red, purple, and/or blue colors in transmitted light. The method comprised subjecting silver halide-containing, photochromic glasses to a specified heat treatment under reducing conditions. Thus, as explained in the patent, the method involved heat treating a silver halide-containing, photochromic glass under reducing conditions at a temperature not exceeding about 450.degree. C. for a time sufficient to develop specific visible light absorption characteristics in the glass. Heat treating temperatures between 200.degree.-450.degree. C. were found to be operable, with temperatures between 350.degree.-450.degree. C. being preferred. The light absorption characteristics developed as a result of the reduction heat treatment are such that the glass demonstrates in the undarkened state a spectral transmittance curve comprising at least one treatment-induced absorption peak having a location and an intensity such that the peak falls within the spectral transmittance region to the right of line CB in FIG. 1 of the drawings. The peak is not present in the parent photochromic glass from which the surface-colored article is fashioned. Accordingly, in the surface colored glass, the surface color differs from the color of the bulk glass (if the bulk glass is colored), a condition that can be readily determined by comparing the spectral transmittance characteristics of the article before and after the removal of a small amount of surface glass therefrom.
The patentees theorized that the surface coloring effects were caused by the chemical reduction of silver in contact with silver halide microcrystals in a region very close to the surface of the glass article, with the identity of the color being determined by the geometric form and arrangement of metallic silver on those microcrystals. Confirmation of that theory was provided via experiments demonstrating that, utilizing a given reduction heat treatment, a particular photochromic glass can display any of a number of absorption peaks depending upon the process initially employed to generate the silver halide microcrystals in the glass. U.S. Pat. No. 4,240,836 is expressly incorporated herein by reference.
Corning Incorporated has marketed photochromic filter glasses derived from three base silver halide-containing, photochromic glass compositions, viz., Corning Code 8111 glass, Corning Code 8122 glass, and Corning Code 8135 glass.
Corning Code 8111 glass has a composition coming within the ranges disclosed in U.S. Pat. No. 4,190,451 (Hares et al.), the glasses described therein consisting essentially, in weight percent, of about 0-2.5% Li.sub.2 O, 0-9% Na.sub.2 O, 0-17% K.sub.2 O, 0-6% Cs.sub.2 O, 8-20% Li.sub.2 O+Na.sub.2 O+K.sub.2 O+Cs.sub.2 O, 14-23% B.sub.2 O.sub.3, 5-25% Al.sub.2 O.sub.3, 0-25% P.sub.2 O.sub.5, 20-65% SiO.sub.2, 0.004-0.02% CuO, 0.15-0.3% Ag, 0.1-0.25% Cl, and 0.1-0.2% Br, wherein the molar ratio of alkali metal oxides:B.sub.2 O.sub.3 ranges about 0.55-0.85, and the weight ratio Ag:(Cl+Br) ranges about 0.65-0.95. Hares et al. further observed that those glasses may also contain up to about 10% total of optional constituents, expressly referring to 0-6% ZrO.sub.2, 0-3% TiO.sub.2, 0-0.5% PbO, 0-7% BaO, 0-4% CaO, 0-3% MgO, 0-6% Nb.sub.2 O.sub.5, 0-4% La.sub.2 O.sub.3 and 0-2% F. Finally, the patentees noted that up to 1% total of transition metal oxide colorants and/or up to 5% total of rare earth metal oxide colorants can be included without adversely affecting the photochromic behavior of the glass. U.S. Pat. No. 4,190,451 is expressly incorporated herein by reference.
Corning Code 8111 glass has the following approximate composition, expressed in terms of parts by weight. However, because the sum of the ingredients closely approaches 100, for all practical purposes the individual values recited may be considered to reflect weight percent.
______________________________________ SiO.sub.2 55.8 Na.sub.2 O 4.0 Ag 0.24 Al.sub.2 O.sub.3 6.5 K.sub.2 O 5.8 Cl 0.20 B.sub.2 O.sub.3 18.0 ZrO.sub.2 4.9 Br 0.13 Li.sub.2 O 1.9 TiO.sub.2 2.2 CuO 0.011 ______________________________________
Corning Code 8122 glass has a composition coming within the ranges claimed in U.S. Pat. No. 4,251,278 (Hares), the glasses described therein being silver halide-containing photochromic glasses wherein about 1-10 ppm palladium and/or gold is included in the compositions. U.S. Pat. No. 4,251,278 refers to two composition regions wherein additions of palladium and/or gold are especially operable. The first region tracks the composition intervals encompassed within U.S. Pat. No. 4,190,451, supra. The second region included glasses consisting essentially, in weight percent, of 40-76% SiO.sub.2, 4-26% Al.sub.2 O.sub.3, 4-26% B.sub.2 O.sub.3, at least one alkali metal oxide in the indicated proportion of 2-8% Li.sub.2 O, 4-15% Na.sub.2 O, 4-15% K.sub.2 O, 8-25% Rb.sub.2 O, and 10-30% Cs.sub.2 O, at least one halogen in the indicated minimum effective proportion of 0.2% chlorine, 0.1% bromine, and 0.08% iodine, and a minimum of silver in the indicated proportion of 0.2% in a glass wherein the effective halogen is chlorine, 0.05% in a glass containing at least 0.1% bromine, but less than 0.08% iodine, and 0.03% in a glass containing at least 0.08% iodine, the sum of those components constituting at least 85% by weight of the total composition. U.S. Pat. No. 4,251,278 is expressly incorporated herein by reference.
Corning Code 8122 glass has the following approximate composition, expressed in terms of parts by weight. In like manner to Code 8111 glass above, however, because the sum of the ingredients closely approaches 100, for all practical purposes the individual values reported may be deemed to represent weight percent.
______________________________________ SiO.sub.2 56.3 K.sub.2 O 5.7 Cl 0.22 Al.sub.2 O.sub.3 6.2 ZrO.sub.2 5.0 Br 0.15 B.sub.2 O.sub.3 18.1 TiO.sub.2 2.2 CuO 0.006 Li.sub.2 O 1.8 Er.sub.2 O.sub.3 0.25 Pd 0.0002 Na.sub.2 O 4.1 Ag 0.21 ______________________________________
Corning Code 8135 glass has at composition included within the ranges disclosed in U.S. Pat. No. 4,390,635 (Morgan), the glasses described therein consisting essentially, in weight percent, of 0-2.5% Li.sub.2 O, 0-9% Na.sub.2 O, 0-17% K.sub.2 O, and 0-8% Cs.sub.2 O, the sum of Li.sub.2 O+Na.sub.2 O+K.sub.2 O+Cs.sub.2 O being 8-20%, 5-25% Al.sub.2 O.sub.3, 14-23% B.sub.2 O.sub.3, 40-65% SiO.sub.2, 0.004-0.02% CuO, 0.15-0.3% Ag, 0.1-0.25% Cl, 0.1-0.2% Br, the molar ratio alkali metal oxide:B.sub.2 O.sub.3 ranging between 0.55-0.85, where the composition is essentially free from divalent metal oxides other than CuO, the weight ratio Ag:(Cl+Br) ranging between about 0.65-0.95, about 0.03-0.25 Cr.sub.2 O.sub.3, and about 0.025-0.3% As.sub.2 O.sub.3 and/or Sb.sub.2 O.sub.3, as analyzed in the glass, wherein over 50% of the copper is present as Cu.sup.+ ions. The patentee observed that up to 10% total of the following optional ingredients in the indicated proportions may also be present: up to 6% ZrO.sub.2, up to 3% TiO.sub.2, up to 1% PbO, up to 7% BaO, up to 4% CaO, up to 3% MgO, up to 6% Nb.sub.2 O.sub.5, up to 4% La.sub.2 O.sub.3, and up to 2% F. Furthermore, up to 1% total of non-oxidizing transition metal oxides and/or up to 5% total of non-oxidizing rare earth metal oxides.
Corning Code 8135 glass has the following approximate composition, expressed in terms of parts by weight. Yet again, however, because the sum of the components closely approaches 100, for all practical purposes the individual values may be considered to represent weight percent.
______________________________________ SiO.sub.2 56.4 K.sub.2 O 5.72 Ag 0.24 Al.sub.2 O.sub.3 6.2 ZrO.sub.2 4.99 Cl 0.215 B.sub.2 O.sub.3 18.1 TiO.sub.2 1.91 Br 0.16 Li.sub.2 O 1.82 NiO 0.144 CuO 0.0057 Na.sub.2 O 4.08 CoO 0.082 ______________________________________
U.S. Pat. No. 4,390,635 is expressly incorporated herein by reference.
U.S. Pat. No. 4,979,976 (Havens et al.) describes a modification of the reduction heat treatment disclosed in U.S. Pat. No. 4,240,836, supra. The patentees observed that an atmosphere of flowing hydrogen had been found to comprise the most effective and efficient environment for the reduction heat treatment of silver halide-containing photochromic glasses to generate surface tints therein. Because of the dangers inherent in using hydrogen, the flow thereof into the heat treating chamber was slow with the consequence that the surface layer developed was not of uniform thickness across all regions of a glass article. Furthermore, a relatively long exposure period, i.e., at least 30 minutes and customarily at least 60 minutes, is required to assure a sufficient depth in the surface layer across all regions of the article. Because the photochromic behavior exhibited by a glass is activated by ultraviolet radiation, the reduced surface layer on the front side of a glass article, for example, the convex side of an ophthalmic lens, must be thin enough to permit the passage of sufficient ultraviolet radiation therethrough to render the article uniformly photochromic. That necessity resulted in the practice termed "front siding". That practice comprises grinding and polishing the front surface of an article to secure a surface layer of uniform thickness across the article, the thickness of the layer being gauged to allow sufficient ultraviolet radiation to pass through into the bulk of the article to activate photochromism therein.
U.S. Pat. No. 4,979,976 discloses a method for producing a reduced surface layer on a photochromic glass article wherein the surface layer will have a uniform thickness across all regions of the article and the thickness can be so controlled that front siding is rendered unnecessary. Moreover, the time required for achieving the surface layer of desired thickness is dramatically reduced.
The patentees produced such a surface layer by initially flowing hydrogen gas into the heat treating chamber at a sufficiently rapid rate to essentially instantaneously fill the chamber with the gas. The flow rate of the gas is thereafter immediately decreased to a velocity permitting careful control of the pace at which surface reduction takes place. The control provided by the method enables a reduced surface layer to be developed on the glass article of sufficient depth to yield the desired coloration, but not so deep as to inhibit the passage of ultraviolet radiation therethrough. In general, the total time required in the process will be on the order of 10-15 minutes.
U.S. Pat. No. 4,979,976 is expressly incorporated herein by reference.
Whereas the three glasses discussed above have been marketed by Corning Incorporated as filter glasses, i.e., glasses cutting off radiation at wavelengths shorter than a specific wavelength, they proved to be unacceptable when subjected to laser radiation of wavelengths within the ultraviolet and up into the blue region of the radiation spectrum.
Accordingly, the principal objective of the present invention was to devise glass compositions transparent to visible radiation, but essentially opaque to ultraviolet radiation, such that they would provide protection against laser radiation in the ultraviolet region of the electromagnetic spectrum and, where desired, up to 550 nm in the visible region thereof, i.e., in the blue region of the spectrum.
A specific objective of the present invention was to fabricate glass lenses which will protect the wearer from eye damage upon exposure to laser radiation.